INSTRUMENTATION
The MicroView™ Scanning Tunneling Microscope
Glassy carbon electrode in solution, coated with copper, deposited and imaged at sub-nanometer resolution.
A New Horizon in Electrochemistry
E
G&G Princeton Applied Research is pleased to open the curtain to a new horizon in research with the MicroView Scanning Tunneling Microscope. The MicroView uses Scanning Tunneling Microscope (STM) technology, which lets you view surfaces at up to atomic resolution. To the STM, we add a built-in potentiostat and electrochemical cell. But the MicroView gives you more than a closeup view. It electrochemically stimulates your sample in situ and measures the resulting reaction as you view a graphic image of the reaction site on your video display. Think of the advantage of using the MicroView to monitor a graphite electrode as it deposits copper onto the surface. Or the value of examining a pit formation with the MicroView as it applies a passivation potential to iron in a chloride solution. So if you're ready for new horizons, call us at 1-800-274-PARC. Our twenty-eight years of experience in electrochemistry tell us that a new day is here.
EG&G
PARC
P.O. BOX 2565 · PRINCETON, NJ 08543-2565 (609) 530-1000 · FAX: (609) 883-7259 Circle 32 for Literature. Circle 33 for Representative.
Figure 5. Optical fiber sensor sensitive to oxygen using second harmonic emission of the diode laser, (a) Total system and (b) sensing device. (Adapted with permission from Reference 28.)
Figure 5 shows a block diagram of an optical fiber sensor sensitive to oxygen. A frequency-doubled beam is focused onto the distal end of an optical fiber, and fluorescence is measured by passing it through a different optical fiber. The conversion efficiency of SHG is 2.5 X 10~6 but it is sufficient as a light source in the optical fiber sensor system (28). The concentration of oxygen is determined at 0-15% levels. A diode laser is made of a nonlinear crystal, so that SHG occurs even in the laser diode itself. The output power obtained is at picowatt levels, but it is still sufficient for use in atomic absorption (29) and molecular fluorescence (30) spectrometries. Visible fluorometry using a frequency-doubled diode laser has wide application because visible fluorometry is already established and in use. However, some of the advantages of near-IR fluorometry (e.g., low background signal) are lost with this approach. Future developments
The technology of the diode laser is progressing rapidly. The output power doubles every year, and the cost is cut in half. A high-power, diode-laserpumped Nd:YAG laser is a hot topic in laser technology because of its high conversion efficiency (10%) from electricity to a coherent light beam. A frequency-doubled Nd:YAG laser producing 80 mW is already commercially
370 A · ANALYTICAL CHEMISTRY, VOL. 62, NO. 6, MARCH 15, 1990
available. Such a laser may be quite useful in future analytical work. On average, the wavelength of the diode laser has been shortened 10 nm every year. This rapid rate of change can be attributed to applications of the laser diode to such commercially successful products as the bar code scanner and the laser printer. We believe that a more powerful laser oscillating at shorter wavelengths will soon appear. Its availability will further extend analytical applications. For recording data to an optical disk, a laser that oscillates at much shorter wavelengths is advantageous because the focused beam diameter can be reduced to the order of the laser wavelength. Thus electronic engineers are concentrating their attention on frequency doubling of the diode laser. Their research has shown that the conversion efficiency of SHG is improved to 14% (24 mW/167 mW) (31). If this diode laser is available as an excitation source for chromatography or electrophoresis detectors, it will become a powerful tool in trace analysis. At present, no commercial diode laser spectrometer is available. We expect that a commercial instrument will appear in the next few years and will find practical analytical usefulness. Its appearance will also help stimulate the development of chemical reagents and analytical procedures for near-IR or deep-red spectrometry.
